Schneider Square D 9036/9037/9038 Electromechanical Liquid Level Controller

In the field of industrial liquid level control, Square D's 9036, 9037, and 9038 series electromagnetic liquid level switches have been widely used for decades for liquid level alarm and pump replacement control in water pumps, oil pumps, condensate tanks, sewage tanks, and hazardous areas due to their simplicity, reliability, and no need for external power supply. Although some models have gradually been replaced by electronic products, a large number of active devices are still in operation, and many OEM devices still specify the use of these classic products. Therefore, mastering its selection, installation, troubleshooting, and maintenance methods is still an essential skill for factory maintenance engineers and system integrators.

This article is based on original technical data and practical application experience to provide you with a complete maintenance guide for Square D liquid level controller. Whether you are dealing with an old 9036 float switch, selecting the 9037 series for a closed pressure tank, or repairing the 9038 mechanical alternators in a dual pump alternating control system, you can find the answer in this article.

Overview of product series and core principles of selection

1.1 Positioning of each of the three series

Class 9036- Open Tank Float Switch

Suitable for atmospheric environments such as open tanks, sewage tanks, cooling towers, etc. Divided into Type D (universal type) and Type G (heavy-duty type), as well as special Type FG (column sewage pump switch). The lever type action mechanism drives the micro switch through the floating ball to rise and fall with the liquid level. We can provide NEMA 1 (indoor universal), NEMA 4 (waterproof and dustproof), and NEMA 7/9 (explosion-proof) enclosures.

Class 9037- Sealed tank float switch

Used for sealing tanks such as pressure vessels, condensate tanks, and daily fuel tanks. Divided into Type E (flange installation) and Type H (2.5-inch threaded installation). The floating ball drives the switch through the connecting rod and adopts PTFE seal or nitrile rubber Quad ring seal, which can withstand a tank pressure of 50 psi. The temperature range is up to 220 ° F (ambient), and the medium temperature can reach up to 250 ° F (Viton) depending on the sealing material.

Class 9038- Mechanical alternators

Specially designed for alternating operation of dual pumps (or dual motors). When the liquid level rises, start one pump first; If the liquid level continues to rise to a high level, the second pump will be put into operation. When the liquid level drops, only the pump that started first stops, and the other continues to run until it reaches a low level. This pure mechanical alternating method avoids the complex wiring and fault risks of electrical alternators. We also offer three types of structures: open tank (Type A), threaded installation closed tank (Type C), and flange installation closed tank (Type D).

1.2 Selection Step 1: Clarify the Tank Type and Installation Method

Before selecting, please answer the following four questions:

Is the tank open or closed?

Open can → 9036 series (or 9038A for alternating)

Sealed tank → 9037 (single pump) or 9038C/D (alternating)

What is the installation interface?

Flange installation → 9037E, 9038D

2.5-inch thread → 9037H, 9038C

Ground or bracket installation → 9036 (optional 9049UMS1 universal installation board)

Environmental hazard level?

Ordinary indoor → NEMA 1

Damp, outdoor, requiring flushing → NEMA 4 (waterproof, dustproof)

Presence of flammable gases or dust → NEMA 7 (Class I, Div 1&2, Groups C, D) and NEMA 9 (Class II, Div 1&2, Groups E, F, G)

What is the required contact action method?

Close the contact when the liquid level rises (for drainage) → standard action (without suffix)

When the liquid level rises, disconnect the contact (for water replenishment) → Form R (reverse action)

Simultaneously provide normally open and normally closed → Form H (only partial 9036GG)

1.3 Electrical Rating Verification

The 9036, 9037, and 9038 series float switches can directly control low-power motors (up to 3 horsepower @ 240V single-phase, 5 horsepower @ 240V three-phase), or control high-power loads through contactors. Please ensure that the rated value of the switch is not lower than the motor nameplate data. For example, the 9036DG2 is rated for 2 horsepower at 115V single-phase and 5 horsepower at 230V three-phase. If used for control circuits (such as PLC inputs), the rated value of the control circuit is 600VA (AC).

For the 9038 mechanical interchanger, its internal N5 or N25 high water level alarm contact (single or double) is a quick action switch, with capacity as shown in Table 3 (e.g. disconnect 6A and connect 7.2A at 120V AC). Do not overload for use.

Correct selection of float and connecting rod - buoyancy and weight calculation

The reliability of the float switch depends on whether the buoyancy generated by the float is sufficient to overcome the resistance of the connecting rod, stop rings, and switch lever. The original factory provides two types of float ball accessory kits (Class 9049):

Tapped at top - the connecting rod is directly screwed into the top of the floating ball. The maximum recommended connecting rod length is 12.5 feet. Suitable for scenarios with small changes in liquid level. Comes with 2 stop rings (one on top and one on the bottom).

Center hole floating ball - The connecting rod passes through the center of the floating ball and can slide on the connecting rod. The maximum connecting rod length can reach 30 feet. Comes with 4 stop rings to provide a wider range of liquid level adjustment.

2.1 Buoyancy data and medium specific gravity correction

All buoyancy data is based on fresh water (with a specific gravity of 1.0) and the float is submerged at 80% (with a 20% safety margin reserved). The net buoyancy of a typical 7-inch 304 stainless steel float is as follows:

Float type net buoyancy (ounces)

Top Attack Style (304SS) 60

Central hole type (304SS) 70

Important: If the specific gravity of the medium is ≠ 1.0, buoyancy must be corrected. For example, if the specific gravity of diesel is about 0.85, the buoyancy is about 85% of that of freshwater. For corrosive liquids or oils, the original manufacturer should be consulted or 316 stainless steel float ball (model suffix S) should be selected.

2.2 Weight Calculation of Connecting Rod and Stop Ring

Each float kit includes a standard 5-foot long connecting rod (material options include brass, aluminum, 304SS). When extending the connecting rod additionally, the total weight needs to be calculated. The following are the unit weights of each material:

Material 5-foot connecting rod weight (ounces) for every additional 1-foot weight (ounces)

Brass 18.5 3.7

Aluminum 6.0 1.2

304 stainless steel 16.9 3.4

Each stop ring weighs approximately 1.5 ounces (2 top attack kits and 4 center hole kits).

Example of buoyancy verification (extracted from original factory data):

The tank is 15 feet deep and uses a center hole float ball, brass connecting rod, and 4 stop rings.

The kit includes a 5-foot connecting rod (weighing 18.5 ounces)+an additional 10 feet (3.7 x 10=37 ounces)+a stop ring 4 x 1.5=6 ounces.

The total downward weight is 18.5+37+6=61.5 ounces.

The net buoyancy of the float is 70 ounces.

Net upward force=70-61.5=8.5 ounces → positive buoyancy, no need for compensating springs.

What if the net buoyancy is negative?

At this point, it is necessary to install a compensating spring (Form C). The compensating spring is installed on the switch lever to provide additional upward lifting force. For example, the 9036 heavy-duty (Type G) factory standard already comes with compensating springs; Other models can be ordered with kits such as 9049A13 (GG), 9049A19 (DG), 9049A20 (DR/DW), etc.

2.3 Maximum Link Length Limit

Exceeding the recommended maximum length may cause the float to fail to reset or the switch to not return. The manufacturer provides the maximum length of compensating springs for different materials:

Material without compensating spring (feet) with compensating spring (feet)

Brass 10 16

Aluminum 25 41

Stainless steel 12 20

Note: The above data applies to the 9038AG1 type alternator. There are slight differences among different switches, please refer to the corresponding table.

Practical steps for installation and debugging

3.1 Installation of 9036 Open Can

Installation position: Ensure that there are no obstacles in the floating ball movement area and that the floating ball does not touch the bottom or side walls of the tank within the range of liquid level changes.

Wiring: Open the switch housing and wire according to the terminal identification (for NEMA 7/9 explosion-proof type, a sealed joint must be used and the housing must be grounded).

Adjust the liquid level action point: Release the stops on the connecting rod, place the float at the desired starting liquid level height, and then lock the stops. For top attack floating balls, the distance between the upper and lower stop rings is the liquid level difference (differential). For the center hole type, the four stop rings can be set with multiple action points such as "pump start", "pump stop", "high position alarm", etc.

Verification action: Manually raise/lower the float, listen for a crisp "click" sound from the switch, and use a multimeter to confirm the continuity of the contacts.

Special note: The connecting rod of the 9036FG30 column switch has a fixed length of 33.75 inches and cannot be extended. The action point is achieved by adjusting the position of the floating ball on the connecting rod. This switch can be converted to reverse action (contact state reversal) on site.

3.2 Installation of 9037 Closed Tank (Type E Flange/Type H Thread)

Sealing inspection: 9037E uses Quad ring sealing, apply a small amount of grease on the sealing ring before installation. The nitrile rubber sealing ring of Type H may harden under long-term high temperature, and it is recommended to replace it every 2 years (spare part 9049Z20 Viton kit can withstand higher temperatures).

Float direction: Refer to the tank drawing to determine the correct orientation of the float. The float position of Type E is divided into three types: 1, 2, and 3, corresponding to the contact action mode (Position 1- liquid lift contact closed; Position 2- liquid lift contact open; Position 3- can be selected by rotating the switch 180 °).

Connecting rod length selection: Select the appropriate length of stainless steel connecting rod (1.75 inches to 12.25 inches) from 9049ER1 to ER12 according to the depth of the tank body. Note that the same switch may require multiple adjustment sizes such as "H", "A", "B", "C", "D", "F", "G", etc. Please refer to the original size chart for details. It is recommended to first measure the range of liquid level changes in the tank, and then compare the table to select the connecting rod number that meets the minimum/maximum travel requirements.

Pressure test: After installation, conduct a pressure test on the tank body (not exceeding 50 psi) to check for any leaks at the seal.

3.3 Special debugging of 9038 mechanical alternators

The core logic of the alternation device:

The liquid level rises to the "first pump start" point → pump 1 runs.

The liquid level continues to rise to the "second pump start" point (high level) → Pump 2 also runs.

The liquid level drops to the "first pump stop" point → pump 1 stops (pump 2 continues to run).

The liquid level drops to a low level (the second pump stops) → Pump 2 stops.

When the liquid level rises next time, it will automatically switch to start pump 2 first and pump 1 as a backup, so as to alternate back and forth.

Debugging steps:

Choose float kit: Open can (9038A) uses 9049A6C center hole float (recommended with compensating spring). The closed tank (9038C/D) uses 9049EF1/EF2 floating balls and corresponding connecting rods.

Set stop rings: The position of the four stop rings determines the start/stop liquid level of the two pumps. According to the size of the tank body, refer to the dimensions of "A", "B", "C", "D", "F", and "G" in the original factory tables 20-23 to locate the stop ring. For example, for 9038DG7 (short hinge pillar), when using 9049ER1 connecting rod, A (minimum stop ring to hinge center distance) is 0.75 inches, and the maximum is 0.63 inches (note that the maximum is less than the minimum? The actual adjustment range given in the table needs to be carefully read). Strongly recommend: Assemble the float and connecting rod outside the tank first, manually simulate the liquid level changes, and use a multimeter to monitor whether the contact alternation sequence is correct.

Optional features:

Manual transfer switch (Form N3) - allows the operator to forcibly specify which pump to start first.

Two level non alternating mode (Form N4) - Cancel the alternating function, only for high and low level control.

High water level alarm (Form N5 single blade/N25 double blade) - triggered when the liquid level exceeds the starting point of the second pump and still does not stop.

Common troubleshooting (required reading for on-site engineers)

Fault 1: The float does not move with the rise of the liquid level

Possible reasons:

Perforation of the floating ball into the liquid (check the weight of the floating ball, the normal 7-inch 304 floating ball is about 0.5 pounds, and if it becomes significantly heavier, water will enter).

The connecting rod is stuck by an obstacle inside the tank.

Insufficient buoyancy (medium density too low or connecting rod too long exceeding buoyancy limit).

Compensation spring failure or not installed.

Solution:

Replace the float (original replacement: 9049AF1/AF2 center hole float, 9049AF3/AF4 top attack float).

Reposition the float path and install guide pipes if necessary.

Recalculate buoyancy, and if there is negative buoyancy, install compensating springs (such as 9049A19, 9049A15, etc.).

Check if the compensating spring is corroded or broken, and replace it with a spring of the same model.

Fault 2: The switch contacts do not switch or do not reset after switching

Possible reasons:

Micro switch wear (especially in high-frequency operation scenarios).

The position of the stop ring is incorrect, resulting in insufficient float travel to trigger the switch.

The switch lever is deformed or the pivot point is rusted.

Solution:

Replace the switch mechanism (spare part number: 9998PC213 for 9036GR/GW series, 9998PC286 for 9036DR/DW series, etc.).

Adjust the position of the stop ring again. The minimum differential travel specified by the original factory is 0.375 inches (standard) or 0.5 inches (reverse action). Measure the actual displacement of the lever using a feeler gauge.

Clean and lubricate the pivot point using lithium based grease.

Fault 3: Leakage at the seal of the 9037 sealed tank

Possible reasons:

The Quad ring seal ring is aging (nitrile rubber has a lifespan of about 2 years at high temperatures).

The flange bolts are not tightened evenly.

The tank pressure exceeds 50 psi.

Solution:

Replace the sealing ring. The original factory provides Viton material kits (Z19, Z20, Z21) with a temperature resistance of up to 250 ° F.

Tighten the bolts in a cross sequence, with torque reference to the flange standard.

If the tank pressure is indeed higher than 50 psi, other types of liquid level transmitters should be used instead.

Fault 4: The 9038 alternator does not alternate and always starts the same pump first

Possible reasons:

The ratchet or slider inside the mechanical alternation mechanism is worn.

The position setting of the stop ring is incorrect, resulting in the first pump stopping point being lower than the second pump starting point, causing logical disorder.

The manual transfer switch (Form N3) is locked in a certain position.

Solution:

Disassemble the casing of the alternator and check if the internal metal slider is flexible. Replace the entire switch mechanism if necessary.

Refer to the original factory tables 20-23 and recalibrate the positions of the four stop rings. Pay special attention to the positive and negative range of the "D" dimension (the distance from the top of the float to the center of the hinge).

If the N3 switch is installed, turn it back to the "automatic" position.

Fault 5: High water level alarm (N5/N25) misoperation or too small dead zone

Possible reasons:

The differential stroke setting of the alarm micro switch is too small.

The float lags behind in movement due to scaling or adhesive media.

Solution:

Increase the spacing between the stop rings (the maximum water level change value provided by the original factory is the alarm dead zone).

Regularly clean the surface of the floating ball (kerosene or specialized cleaning agents can be used for oily media).

Maintenance cycle and spare parts management

5.1 Routine Preventive Maintenance

Periodic tasks

Visually inspect the float ball connecting rod monthly for any obvious bending or corrosion; Listen to whether the sound of the switch action is crisp.

Manually operate the float every season and test the contact resistance of the contacts with a multimeter (which should be less than 0.1 ohms). For sealed tanks, observe whether the external indicator pointer matches the actual liquid level.

Inspect the switch chamber annually to remove internal dust and moisture; Replace the nitrile rubber sealing ring (9037/9038C, etc.). Verify buoyancy - immerse the float in water and test whether it can lift a weight of the specified weight.

5.2 Recommended spare parts list

The following are on-site replacement parts that should be kept on hand (based on the original 9998 and 9049 series):

Spare part number applicable model description

9049A6C 9036D/G, 9038A center hole float ball kit (including 5ft brass rod, 4 stop rings)

9049A13 9036GG compensation spring

9049EF1 9037E, 9038D 304SS floating ball (without connecting rod)

9049ER5 9037E, 9038D 5.25-inch stainless steel connecting rod

9049Z20 9037H, 9038C Viton sealing kit (high temperature resistant)

9998PC214 9036GR/GW (reverse action) switch mechanism assembly

9998PC216 9036GW housing sealing gasket

5.3 Response strategies for discontinued products

For equipment such as 9035 and early 9036 produced before 1965, the original factory no longer provides spare parts. At this point, it is recommended to replace the entire device with a new electronic level switch (such as Square D's 9012 series or other brands). If it is necessary to maintain the original installation dimensions, the 9036G can be replaced with the old 9036A using the 9049UMS1 universal installation bracket. For the 9038 interchanger, it is possible to consider using a PLC to achieve electrical alternation, but the float switch needs to be retained as the liquid level sensor.